A multiplexer includes a transmission-side filter connected to a common terminal and a transmission input terminal, and a reception-side filter connected to the common terminal and a reception output terminal, in which the transmission-side filter includes serial arm resonators, parallel arm resonators, and a parallel arm circuit. In an interdigital transducer electrode included in the serial arm resonator connected closest to the common terminal, an electrode finger pitch at a center portion in an arrangement direction of electrode fingers is maximum among electrode finger pitches of the interdigital transducer electrode, and electrode finger pitches at end portions in the arrangement direction are minimum among the electrode finger pitches of the interdigital transducer electrode.

A SAW resonator comprises two reflectors and a transducer arranged between the reflectors. A resonant space between the transducer and a respective reflector is set large enough to enable occurrence of main resonance and at least one further resonance of comparable admittance. Thus, a multiple resonant resonator is achieved that can be used as a parallel resonator in a filter circuit with a DMS track for example to improve attenuation in a stop band.

Reduced-size guided-surface acoustic wave (SAW) resonators are disclosed. Guided-SAW resonators can achieve high acoustic coupling and acoustic quality Q, but may have a larger surface area compared with a traditional temperature compensated (TC)-SAW resonator. In an exemplary aspect, a guided-SAW device is fabricated with a metal-insulator-metal (MIM) capacitor to produce a guided-SAW which has the same high Q with a surface area which is the same or less than traditional TC-SAW resonators.

An acoustic wave filter includes a piezoelectric substrate, first and second input-output terminals, and a longitudinally coupled resonator unit in a path connecting the first and second input-output terminals to each other, and the resonator unit includes five or more interdigital transducer electrodes aligned in an acoustic wave propagation direction, the IDT electrodes include a center IDT electrode at the center in the propagation direction and first and second IDT electrodes at symmetric or substantially symmetric positions in the propagation direction with respect to the center IDT electrode, each of the first and second IDT electrodes includes a main pitch portion and a pair of narrow-pitch portions provided between the main pitch portion and both ends of the IDT electrode in the propagation direction, and the first and second IDT electrodes differ from each other in the number of electrode fingers of the main pitch portion.

A filter includes a parallel arm resonator and an interdigital capacitor. The parallel arm resonator has an IDT electrode defined by first electrode fingers. The interdigital capacitor is defined by second electrode fingers and is connected to the parallel arm resonator. The electrode finger pitch of the second electrode fingers is smaller than the electrode finger pitch of the first electrode fingers. The film thickness of the second electrode fingers is smaller than the film thickness of the first electrode fingers. A self-resonant frequency of the interdigital capacitor is higher than a pass band of the filter.

A filter device includes a first filter connected between a common terminal and a first individual terminal, and a second filter connected between the common terminal and a second individual terminal. A pass band of the second filter is in a frequency range lower than a pass band of the first filter. The first filter includes SAW resonators, at least one of which includes divided resonators connected in parallel with each other. Each of the divided resonators includes an IDT. A pitch of the IDT of one of the divided resonators is different from that of another of the divided resonators.

In a resonator, two interdigital transducers (W1,W2) are electrically series-connected and arranged next to each other in the longitudinal direction within an acoustic track delimited by reflectors. Between the two interdigital transducers, a transition area (UEB) is formed in that the finger period p, which is defined as the distance between the finger centers of adjacent transducer fingers, is higher in comparison to the remaining interdigital transducer.

Aspects of this disclosure relate to an acoustic wave resonator having at least two resonant frequencies. An acoustic wave filter can include series acoustic wave resonators and shunt acoustic wave resonators together arranged to filter a radio frequency signal. A first shunt resonator of the shunt acoustic wave resonators can include an interdigital transducer electrode and have at least a first resonant frequency and a second resonant frequency. Related acoustic wave resonators, multiplexers, wireless devices, and methods are disclosed.

An acoustic resonator includes a piezoelectric plate with a back surface attached to a substrate. An interdigital transducer (IDT) including interleaved fingers is formed on the front surface of the piezoelectric plate, the IDT comprising multiple copies of a unit cell juxtaposed along a length of the IDT. Each unit cell includes a first pitch/mark zone having a first pitch P1 between adjacent fingers and a first mark M1 and a second pitch/mark zone having a second pitch P2 and a second mark M2, where P.sub.2 is not equal to P.sub.1 and M.sub.2 is not equal to M.sub.1. A radio frequency signal applied to the IDT causes the first pitch mark zone and the second pitch/mark zone to excite a same shear primary acoustic mode in the piezoelectric plate.

A surface acoustic wave filter includes resonators, wherein one of the resonator includes four or more regions with different pitches of electrode fingers, the pitch of electrode fingers in each of the four or more regions is constant, the pitch of electrode fingers in first regions, among the four or more regions, disposed at both ends of the resonator in a surface acoustic wave propagation direction is smaller than the pitch of electrode fingers in the regions other than the first regions, and the pitch of electrode fingers in a second region adjacent to the first region and the pitch of electrode fingers in a third region adjacent to the first region are different from each other.